Mobile oscillating spot grinder with pressure control means to produce a feathering effect

ABSTRACT

A swing-type grinder for conditioning the surfaces of horizontally disposed metal plates by removing defects such as pits, rolled-in scale, cracks and other minor blemishes. A mobile carriage for the grinder includes a frame which supports the grinding wheel via a vertical shaft from which depends a horizontal shaft pivotably carrying a support member for the grinding wheel. A pair of hydraulic cylinders alternately pull wire-rope members which partially surround a pulley connected to the top of the vertical shaft causing it to oscillate. The horizontal shaft provides limited vertical pivotable movement by the grinding wheel which is spaced forward of the vertical shaft and carried by a vertical axle which revolves in a bearing, the horizontally disposed grinding wheel being at the axle&#39;&#39;s lower aspect. The casing for the axle&#39;&#39;s bearing is at the forward end of the support member which depends at its after end from the horizontal shaft. An electric motor is carried centrally on the support member which drives the grinding wheel by a pair of matched endless belts. The weight of the support member is counter-balanced by a horizontal compression spring. An upright hydraulic cylinder is pivotably attached to the frame above the grinding wheel and has a piston with a depending piston rod which connects to the bearing casing for the grinding wheel&#39;&#39;s vertical axle. The upper portion of this hydraulic cylinder is connected into a closeable hydraulic circuit which contains a pair of piston-type accumulators. When the grinding wheel is oscillated from side to side via oscillations of the vertical shaft produced by the pair of horizontal hydraulic cylinders, the downward force on the grinding wheel decreases as the grinding wheel moves outwardly from a central location due to the piston rod being pulled out of the cylinder and thus providing more space above the piston in the cylinder for hydraulic fluid in the closed hydraulic circuit with the pressure from the accumulators being proportionately decreased as a result. Consequently, a feathering-type action automatically takes place with the sideto-side movement of the grinder wheel so that the spot being ground is blended with the surrounding plate. Hand controls exist for increasing or decreasing the fluid in the closed circuit and for opening the closed circuit. Also, the arc of oscillation by the grinding wheel is adjustable.

United States Patent [1 1 Daiuta 1 MOBILE OSCILLATING SPOT GRINDER WITH PRESSURE CONTROL MEANS TO PRODUCE A FEATHERING EFFECT [75] lnventor: Leo R. Daiuta, Kennett Square, Pa.

[73] Assignee: Lukens Steel Company, Coatesville,

[22] Filed: Nov. 21, I974 [21] Appl. No.: 525,749

[52] U.S.Cl ..5I/I70 T;5l/55;5l/l77 [51] Int. Cl B24b 23/02 [58] Field of Search 51/170 R, 170 T, 174,177,

[56] References Cited UNITED STATES PATENTS 1,063,222 6/1913 Small 51/55 2,629,210 2/1953 Robinson r 51/177 2,799,974 7/1957 Andrysick 51/55 Primary Examiner-Al Lawrence Smith Assistant ExaminerNicholas P. Godici Attorney, Agent, or Firm-Mason, Mason & Albright [57} ABSTRACT A swingtype grinder for conditioning the surfaces of horizontally disposed metal plates by removing defects such as pits, rolled-in scale, cracks and other minor blemishes. A mobile carriage for the grinder includes a frame which supports the grinding wheel via a vertical shaft from which depends a horizontal shaft pivotably carrying a support member for the grinding wheel. A pair of hydraulic cylinders alternately pull wire-rope members which partially surround a pulley connected to the top of the vertical shaft causing it to oscillate. The horizontal shaft provides limited vertical pivotable movement by the grinding wheel which is spaced forward of the vertical shaft and carried by a vertical axle which revolves in a bearing, the horizontally disposed grinding wheel being at the axles lower aspect. The casing for the axles bearing is at the forward end of the support member which depends at its after end from the horizontal shaft. An electric motor is carried centrally on the support member which drives the grinding wheel by a pair of matched endless belts. The weight of the support member is counterbalanced by a'horizontal compression spring. An upright hydraulic cylinder is pivotably attached to the frame above the grinding wheel and has a piston with a depending piston rod which connects to the bearing casing for the grinding wheels vertical axle. The upper portion of this hydraulic cylinder is connected into a closeable hydraulic circuit which contains a pair of piston-type accumulators. When the grinding wheel is oscillated from side to side via oscillations of the vertical shaft produced by the pair of horizontal hydraulic cylinders, the downward force on the grinding wheel decreases as the grinding Wheel moves out' wardly from a central location due to the piston rod being pulled out of the cylinder and thus providing more space above the piston in the cylinder for bydraulic fluid in the closed hydraulic circuit with the pressure from the accumulators being proportionately decreased as a result. Consequently, a feathering-type action automatically takes place with the side-to-side movement of the grinder wheel so that the spot being ground is blended with the surrounding plate. Hand controls exist for increasing or decreasing the fluid in the closed circuit and for opening the closed circuit. Also, the arc of oscillation by the grinding wheel is adjustable.

8 Claims, 4 Drawing Figures PATENTED SEP 9 I975 SHEET 1 [1F 3 FIG. 2

PATENTED SEP 9 I975 FIG. 3

SHEET 2 OF PATENTED 9|975 3, 903 .658

sumsu g Q E. H E 2 s5 FIG.4

MOBILE OSCILLATING SPOT GRINDER WITH PRESSURE CONTROL MEANS TO PRODUCE A FEATHERING EFFECT BACKGROUND OF THE INVENTION In conditioning plate surfaces, defects such as pits, rolled-in scale, cracks, seams and other minor blemishes are usually ground out manually by use of portable hand grinders driven either by air or electrically. In spot grinding, only the areas where defects occur are ground. To avoid any sharp hollowed-out areas, the operator must sweep his grinder in a smooth are. In addition, he must blend the depth of the ground out area gradually up to the surface of the plate in all directions. This action is known as feathering" and is accomplished by raising the grinding wheel at the end of each arc sweep. An efficient spot grinding operation comprises the maintenance of a high rate of metal removal during the contact time, swinging of the grinding wheel in a smooth arc during the operation, feathering, and maintaining a long length of contact time compared with non-contact time. At present, all four items are accomplished manually and consequently are subject to the physical limitations of the human operator.

A need exists and has existed for some time, particularly in the steel industry, for a grinder which will permit an operator to accomplish automatically or semiautomatically the same function with the same results presently obtainable manually, but at a higher rate of speed, with increased metal removal, variable controlled feathering in any direction on the plate, and which will decrease the fatigue factor for the operator and permit a longer contact time.

SUMMARY OF INVENTION The invention relates to a mechanized semiautomated spot grinder for removing defects from horizontally disposed metal plate surfaces. In particular, it relates to such a spot grinder wherein the desired degree of feathering can be automatically and variably controlled by the operator.

In accordance with the present invention, a spot grinding wheel is mechanically mounted on a movable frame which is operable by one man. The invention permits use of higher horse-power energy input and thus increases the metal removal rate. In the invention, the swinging of the grinder wheel is powered and controls for variable length strokes are included. In addition, provision is made for a mechanized variably controlled feathering of the grinding wheel in any direction on the plane of grinding. In consequence, the fatigue factor for the operator of the spot grinder is considerably reduced and he is enabled to be both more effective and efficient in spot grinding operations.

The feathering action of the grinding wheel according to the invention is accomplished by a closed hydraulic circuit which reduces the downward force on the grinding wheel as it moves outwardly from over the blemish being ground. Downward force on the grinder is accomplished by means of a hydraulic cylinder, piston, piston rod assembly which is connected so as to apply downward force on the grinding wheel with one end of the assembly connected to the supporting frame. Within the hydraulic circuit, a pair of accumulators are provided. With the grinding wheel in central position, desired pressure is obtained in the hydraulic circuit which is then closed. Thereafter, as the grinding wheel is energized and sweeps back and forth, the cylinder forces the grinding wheel against the plates surface. However, at the same time the cylinder swivels about its suspension point on the frame and in so doing the piston is moved relatively downwardly increasing its stroke length relative to the cylinder. As such length increases, more hydraulic fluid is fed into the cylinder by the precharged accumulators. Inasmuch as the hydraulic circuit is isolated, the pressure of the system is thereby decreased, When the swing is reversed, the pressure increases to its previous level as the grinding wheel returns to the central position. Thus, the grinding force follows a curve from maximum when the grinding wheel is in its central position and the hydraulic cylinder assembly is vertically disposed to minimum when the grinding wheel is at the end of its oscillation movement in one direction. Inasmuch as the grinding energy is proportional to the downward force on the grindwheel, the amount of metal removal and the shape of the grinding wheel indentation into the plate surface corresponds to the force curve which results thereby providing the feathering action.

The accumulators used in the system can be either pneumatic or mechanical. Their size and the volume of the cylinder above the piston determines the initial shape of the forced curve. The addition of the hydraulie system gives the operator a highly flexible means of changing the shape to suit the depth of the defect and desired feathering shape during the grinding operation. This can be accomplished quickly through manipulation of the hydraulic controls.

The hydro-pneumatic capacity and pressure requirements for the system are comparatively small which permits the use of a compact system in units of cubic inches required and a relatively small horsepower. Thus, the invention is highly adaptable for the design of an economical and flexible piece of equipment, the provision of which is the major object of this invention.

Other objects, adaptabilities and capabilities of the invention will be appreciated by those skilled in the art as the description progresses, reference being bad to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a spot grinder in accordance with the invention with the handle (except for a portion) removed for the purpose of clarity;

FIG. 2 is a diagrammatic representation of the hydraulic circuit of the invention;

FIG. 3 is a sectional view of the spot grinder taken on lines 33 of FIG. 1; and

FIG. 4 is a diagram of the grinding wheel force on the plate illustrating the force curve obtainable by means of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the swing-type grinder designated generally by reference numeral 10 comprises a frame ll which is constructed of a pair of parallel channel bars 12 and 14 connected by an upstanding forward plate 15, in part by further upstanding centrally located plates 16 and by a rear bar 17. Each channel beam 12 and 14 has wheel mountings 20 and 21 rigidly attached thereto by welding other suitable means. A horizontal axle 22 extending inwardly from each wheel mounting and 21 receives a freely rotatable wheel 24.

Extending across plates 15 and 16 and rigidly connected thereto is a large channel piece 25 which has affixed thereto on the upper portion of each of its vertical limbs, horizontal guide members 26.

Connected to the horizontal portion of the channel piece 25 are a pair of hydraulic members which include cylinders 27, conventional internal pistons 28 and attached piston rods 30. Each piston rod 30 is connected on its outer end to a clevis socket assembly 31 from which extends a pair of wire ropes 32 to be received around a pulley 34; wire ropes 32 return to the clevis socket 31 assembly of the piston rod 30 of the other hydraulic cylinder member 27 whereby by alternately actuating the cylinder members 27, pulley 34 is caused to be rotated through an angle in first one direction and then the other. Firmly attached to the pulley 34 by a spline or other suitable means is a vertical pivot member 35 which is encircled by ball bearings 36 and is rigidly connected on its lower end to a horizontal pivot means comprising a shaft 37. A casing 40 surrounds the pivot member 35 and bearings 36, the latter being spaced apart by a spacer cylinder 41. Snap rings 42 and bushings 44 serve to retain bearings 36 in their desired relative position. Casing 40 is preferably firmly attached to the bottom of the channel piece 25.

The grinding wheel 86 is carried by a support member 45 which comprises a pair of spaced upright plates 46 (only one being shown in the figures) which are rigidly connected by a pair of transverse vertical plates, a forward plate 47 and after plate 48. Plates 46, 47, 48 surround an electric motor 50 which is carried on a bottom plate 51 of support member 45 rigidly connected to plates 46, 47 and 48. A stiffening plate 52 is rigidly connected to the after plate 48 which together with a rigidly connected horizontal plate 54 carries bearing members 55 (only one of which is shown in FIG. 3) which each receive shaft 37. An alignment bar 56 is vertically disposed and connected rigidly to pivot member 35. in its upper aspect, bar 56 is connected to a horizontal piece 60 which includes a circular portion 61 for rigidly grasping the vertical pivot member 35. Centrally, bar 56 is connected to the lower aspect of pivot member 35 via strut 57. At the lower aspect of bar 56 a bushing 62 holds a nut 64 which carries a rubber bushing 65 with an opening to receive a shaft 66 having an enlarged cylindrical portion 67 threadably receiving a shaft 70 which includes an eye 71 surrounding a rubber bushing 72 with an opening to receive bolt 74 which is also received through a further opening at the after end of the plate 51 and secured in place by a nut 75. A compression spring 76 has one end bearing against the enlarged cylindrical portion 67 and the other against a washer 77 which surrounds shaft 66 and bears against the rubber bushing 65. The strength of compression spring 76 is such that it counterbalances the weight of support member 45.

Motor 50 is secured on the bottom plate 51 of support member 45 and includes a shaft 80 which vertically extends through an opening made for such purpose in bottom plate 51. Shaft 80 has a pulley 81 connected thereto by splines or other suitable means.

At the forward end of support member 45, a bearing casing 82 is rigidly connected through a bar 83 of T- cross-section welded thereto which is bolted to forward plate 47 by bolts 49. Casing 82 receives a vertically disposed shaft comprising the grinding wheel axle 84. The lower aspect of axle 84 is threaded to receive a nut 85 which urges a grinding wheel 86 against a protector piece 87 which, in turn, is received on its upper side against a shoulder 90 provided in axle 84 and on its lower side against the grinder cover 91.

Secured in place above protector piece 87 is a sheave 92 which is adapted to receive a pair of matched grip belts 94 also received by pulley 81 so that rotation of pulley 81 by motor 50 causes sheave 92 to rotate via belts 94, the sheave 92 being firmly connected to axle 84 whereby it also rotates and causes the rotation of grinder wheel 86.

Axle 84 is mounted in bearing casing 82 by means of a pair of double ball bearing assemblies 95 which are held in place on one side by an enlarged portion 96 of axle 84. Portion 96 is surrounded by a spacer member 97 held rigid with casing 82 by means ofa dowel which is not shown. A lock washer 100 is mounted between the upper assembly 95 and a bearing lock nut 102 which is secured in the position shown on upper aspect of axle 84. Casing 82 includes a cover 102 which is fastened thereon by means of bolts 104. Casing 82 also includes a projection 105 in its forward upper aspect which moveably but firmly receives the depending end of a piston rod 106 having its other end attached to a piston 108 within the hydraulic cylinder 107.

Plate 15 of frame 11 has connected thereto a pair of extensions 110 which rotatably receive shafts 111 which in turn support a yoke 112. By means of a pair of further shafts 114, in the forward and after portions of yoke 112, block 115 is carried. Block 115 is adapted to receive and support cylinder 107. As a result, cylinder 107 is movable in an arc about a horizontal axis delined by the shafts 111, the axis thereof being disposed normally to channel beams 12 and 14 of frame 11, and is further movable in an are about an axis defined by shafts 114 which is somewhat inclined from the horizontal as may be seen in the figures and falls within a vertical plane which is perpendicular to plate 15.

A handle part 116, a portion of which is shown in FIG. 1, connects to lugs 117 extending from plate 15 and the bottom portions of channel beams 12 and 14.

An oscillation control assembly 120 includes a pair of projections 121 on either side whereby it can be selectively moved forward and aft in the guide member 26. Each projection 121 is held snugly in the guide member 26 by means of a compression spring 122. The projections 121 are moved outwardly so they are no longer in contact with guide member 26 by gripping a lever 124 which is linked to projection 121 and extends relative to the handle 123 of control assembly 120. It will be noted that a horizontal plate 125 is included in control assembly 120 from which depends a pair of side-by-side switches 126, only one of which is seen in FIG. 3. Spaced levers 127 connect to switches 126, such levers each including contact rollers 130 which are actuated by contact with an oscillation bar 131 which rigidly connects to the vertical pivot member 35 and is received between rollers 130. Switches 126 are electrically connected to solenoids 132 which control a hydraulic valve 134 for reversing the movement of piston rods 30. Thus, the closer that control member 120 is to the pivot member 35, the larger the arc of oscillation permitted for oscillation rod 131 and accordingly the arc of oscillation by the support member 45 and the grinding wheel 86 is correspondingly increased by movement of control member 120 to the right as seen in FIGS. 1 and 3 and decreased by movement to the left.

Frame 11 of grinder carries in its after portion a hydraulic power unit 135 which includes a relief valve 136. As will be understood from HO. 2, power unit 135 comprises a hydraulic pump rated 2.25 GPM at 900 psi max. driven by a 2 HF. squirrel cage conduction motor 137 and includes a suction strainer 140 which draws hydraulic fluid from the sump 141. The outlet of hydraulic pump 142 delivers through a hydraulic outlet line 144 hydraulic fluid under pressure: (1) to the aforementioned valve 134, which controls the alternating forward and aft movement of piston rods 30, and (2) to a further valve 146 which controls the downward pressure on piston 108 in cylinder 107 and thus the downward force of piston rod 106. Valve 146 may also be used to remove entirely hydraulic pressure from the system.

The rate of oscillation by pistons 28 is controlled by an adjustable restricter valve 147 which is in hydraulic pressure line 144 prior to valve 134.

It will be observed from FIG. 2, that cylinder 107 is in a closed hydraulic circuit designated 144a depending upon the position of the valve 146. This hydraulic circuit 144a includes a check valve 150 to ensure circulation of hydraulic fluid in the circuit, a globe valve 151 for maintenance draining of the system, a pressure gauge 152, a relief valve 154, and a pair of flexible hoses 155 which lead into and away from the upper portion of cylinder 107. Also included in the hydraulic circuit 144a is a pair of accumulators 160 of the piston type, one of which is connected into the circuit 144a by means of a valve 161. A third accumulator 160 with a connecting valve 161 may be optionally included as shown in dot-dash lines.

The wiring for grinder l0 and the specific location of hydraulic lines, valves and the like are not shown inasmuch as this is largely a matter of choice and well within the skill of the art. However, in general, the wiring is routed on one side of grinder 10 and the hydraulic lines, insofar as possible, on the other. Where this is not possible, the wiring is maintained above the hydraulic lines. Preferably, the valves 146 and 134 are located on or conveniently close to the end of handles part 116 and the valves 147 and 161 also are preferably located on handle part 116 or elsewhere provided they can be controlled with facility by the operator of grinder 10.

In operation, the grinder 10 is manually rolled on wheels 24 to a location on a horizontal metal plate which has a blemish to be removed and the grinding wheel 86 in its central location is placed over the blemish. Motor 50, if not already energized is switched on and oscillation control 120 is set as desired. Adjustable restrictor valve 147 is also set to control the speed of the oscillation and the valve or valves 161 of accumulators 160 are opened or closed for the desired feathering action. In this connection, it will be appreciated that adjustable restrictor valve 147 causes the oscillation to be at a reduced rate by making the restriction in such valve smaller and the rate is increased by enlarging same. The opening of valve or valves 161 increases the effective length of the feathering action.

With the grinder 10 in place as described above, the power unit 135 if not already started is energized whereupon by the alternating energizing of solenoids 132 clue to the sweeping action of the oscillation rod 131 coming into contact with roller contacts 130, switches 126 first energize one solenoid 132 and then the other solenoid 132. Valve 146 is moved to the left relative to the position shown in FIG. 2 until pressure gauge 152 indicates the desired pressure has been reached in hydraulic circuit 144a whereupon this valve is closed by placing it in its central position to isolate hydraulic circuit 144a. The grinding wheel support 46 is oscillated from side to side by action of the vertical pivot member 35 through wire ropes 32 connected to the piston rods 30 of cylinders 27. A downward force is created on grinding wheel 86 by the internal pressure of the hydraulic fluid in cylinder 107. As support member 45 and grinding wheel 86 are oscillated from side to side the piston rod 106 moves the piston 108 whereby it alternately enlarges and reduces the volume in cylinder 107 above piston 108. This in turn causes a reduction or increases of pressure in the closed hydraulic circuit 144a proportional to such increase or reduction of volume. As the volume is increased, hydraulic fluid is forced into the cylinder by the cut-in accumulators which, due to the expansion within same, cause a decrease in pressure within circuit 1440. In contrast, as the piston 108 moves upwardly in the cylinder 107, the volume is reduced and hydraulic fluid is forced back into cut-in accumulators 160 which results in increased pressure in the circuit 144a and on the piston 106. This increase and decrease is indicated diagrammatically in FIG. 4 by the arrow 164 which produce a force curve indicating the feathering action which automatically takes place due to the above described action.

The operator may optionally move the valve 146 to the right momentarily as seen in FIG. 2 whereby a bleed ofa small amount of hydraulic fluid from circuit 1440 takes place and the pressure as indicated by gauge 152 decreases. By so doing, the forced curve 165, as shown in FIG. 4, becomes more shallow. This can be continued until insufficient force exists to maintain the grinding wheel 86 on the surface because the counter force from compression spring 76 overcomes the downward pressure exerted on the piston 108.

Although the above description sets forth the preferred embodiment of my invention, it is to be understood that it is capable of other adaptations and modifications without departing from the spirit of the invention as set forth within the scope of the following claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A swing-type grinder for removing from a horizontal surface defects such as pits, cracks and other minor blemishes the grinder comprising: a grinding wheel; a frame for carrying said grinding wheel; support means for said grinding wheel connected to said frame, said support means including substantially vertically disposed first pivot means and substantially horizontally disposed second pivot means whereby said grinder wheel is adapted to be moved both horizontally and vertically relative to said frame; oscillation producing means connected to said support member whereby said support member with said grinding wheel is adapted to be selectively oscillated relative 'to said first pivot means and said grinding wheel is moved from side to side relative to a central position; a hydraulic cylinder means including a cylinder, a piston and a piston rod extending from the cylinder interconnected with said grinding wheel and said frame for establishing the force which said grinding wheel bears against the underlying surface, the connection being such that the piston of said hydraulic cylinder means moves therein in response to horizontal movements, said hydraulic means being extended in length as said grinding wheel is oseillated away from its central position; said hydraulic cylinder means being in a closed hydraulic circuit which includes at least one accumulator whereby said force of said grinding wheel against the underlying surface is reduced by said oscillating movement as said grinding wheel is moved away from its said central position.

2. A grinder in accordance with claim 1, wherein said piston rod is interconnected to said grinding wheel and said cylinder is interconnected to said frame.

3. A grinder wheel in accordance with claim 2, wherein said hydraulic circuit is connected into said cylinder above said piston.

4. A grinder in accordance with claim 1, wherein said frame is mounted on wheels.

5. A grinder in accordance with claim 1, wherein said grinding wheel comprises a horizontally disposed disc.

6. A grinder in accordance with claim 5, wherein said disc revolves around a vertical axle which is supported by bearings provided in said support means whereby said axle is maintained in a vertical position and said disc is maintained in a horizontal position throughout said oscillation.

7. A grinder in accordance with claim 1, wherein a motor is carried by said support means, said motor being connected to said grinding wheel for rotating same by at least one endless belt.

8. A grinder in accordance with claim 1, including means for counterbalancing the weight of said support member. 

1. A swing-type grinder for removing from a horizontal surface defects such as pits, cracks and other minor blemishes the grinder comprising: a grinding wheel; a frame for carrying said grinding wheel; support means for said grinding wheel connected to said frame, said support means including substantially vertically disposed first pivot means and substantially horizontally disposed second pivot means whereby said grinder wheel is adapted to be moved both horizontally and vertically relative to said frame; oscillation producing means connected to said support member whereby said support member with said grinding wheel is adapted to be selectively oscillated relative to said first pivot means and said grinding wheel is moved from side to side relative to a central position; a hydraulic cylinder means including a cylinder, a piston and a piston rod extending from the cylinder interconnected with said grinding wheel and said frame for establishing the force which said grinding wheel bears against the underlying surface, the connection being such that the piston of said hydraulic cylinder means moves therein in response to horizontal movements, said hydraulic means being extended in length as sAid grinding wheel is oscillated away from its central position; said hydraulic cylinder means being in a closed hydraulic circuit which includes at least one accumulator whereby said force of said grinding wheel against the underlying surface is reduced by said oscillating movement as said grinding wheel is moved away from its said central position.
 2. A grinder in accordance with claim 1, wherein said piston rod is interconnected to said grinding wheel and said cylinder is interconnected to said frame.
 3. A grinder wheel in accordance with claim 2, wherein said hydraulic circuit is connected into said cylinder above said piston.
 4. A grinder in accordance with claim 1, wherein said frame is mounted on wheels.
 5. A grinder in accordance with claim 1, wherein said grinding wheel comprises a horizontally disposed disc.
 6. A grinder in accordance with claim 5, wherein said disc revolves around a vertical axle which is supported by bearings provided in said support means whereby said axle is maintained in a vertical position and said disc is maintained in a horizontal position throughout said oscillation.
 7. A grinder in accordance with claim 1, wherein a motor is carried by said support means, said motor being connected to said grinding wheel for rotating same by at least one endless belt.
 8. A grinder in accordance with claim 1, including means for counterbalancing the weight of said support member. 